Re: [Intel-gfx] [PATCH] drm/i915/userptr: restore probe_range behaviour

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 25/10/2022 16:54, Matthew Wilcox wrote:
> On Tue, Oct 25, 2022 at 04:40:23PM +0100, Tvrtko Ursulin wrote:
>>
>> On 24/10/2022 18:21, Matthew Auld wrote:
>>> The conversion looks harmless, however the addr value is updated inside
>>> the loop with the previous vm_end, which then incorrectly leads to
>>> for_each_vma_range() iterating over stuff outside the range we care
>>> about. Fix this by storing the end value separately.
>>>
>>> Testcase: igt@gem_userptr_blits@probe
>>> Fixes: f683b9d61319 ("i915: use the VMA iterator")
>>> Reported-by: kernel test robot <oliver.sang@intel.com>
>>> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
>>> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
>>> Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
>>> Cc: Vlastimil Babka <vbabka@suse.cz>
>>> Cc: Yu Zhao <yuzhao@google.com>
>>> ---
>>>    drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 3 ++-
>>>    1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
>>> index b7e24476a0fd..dadb3e3fa9c8 100644
>>> --- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
>>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
>>> @@ -427,9 +427,10 @@ probe_range(struct mm_struct *mm, unsigned long addr, unsigned long len)
>>>    {
>>>    	VMA_ITERATOR(vmi, mm, addr);
>>>    	struct vm_area_struct *vma;
>>> +	unsigned long end = addr + len;
>>>    	mmap_read_lock(mm);
>>> -	for_each_vma_range(vmi, vma, addr + len) {
>>> +	for_each_vma_range(vmi, vma, end) {
>>>    		/* Check for holes, note that we also update the addr below */
>>>    		if (vma->vm_start > addr)
>>>    			break;
>>
>> I am unsure of the for_each_vma_range() behaviour regarding holes. If it
>> just skips overs them and continues to next VMA in the range then patch
>> looks good to me. Could someone confirm?
> 
> It's "For each VMA in this range".  It doesn't iterate over non-VMAs
> within that range ;-)  Nor does a gap between VMAs stop the iteration.

Thank you Matthew - I ventured briefly into the maple leaf world but 
quickly decided it would be much easier to ask. :)

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko